The economic damage caused by the corrosive effect of the oxidation of galvanically active metals cannot be underestimated in civil engineering applications. Bridges, parking decks, balconies, and other reinforced concrete structures are continually susceptible to weakened structure due to corrosion of reinforcing metals within such concrete structures.
Weakened structure is caused in one circumstance by corroded reinforcing bars (also known as rebars) that occupy a greater volume than uncorroded rebars. The greater volume occupied by the corroded rebars produces tension in the concrete, which causes cracks. Cracks permit more corrosion due to additional exposure to salts penetrating the volume of the concrete. A vicious cycle of corrosion, tension, and cracking accelerates until the structure fails.
To combat the deterioration of reinforcing metallic structures within concrete, the art has developed sacrificial galvanically active metal/adhesive anodic tape systems for cathodic protection of reinforcing bars in concrete structures. These anodic tape systems are designed to sacrifice a metal such as zinc in a galvanic circuit created by electrical connection of the reinforcing metallic bars having a substantial iron content and zinc which is affixed to the concrete by an ionically-conductive agent, usually a pressure-sensitive adhesive. However, deficiencies exist in this system such that cathodic protection of the reinforcing bars ceases prior to the complete sacrifice of the zinc metal. Useful life of a cathodic protection system is dependent on the thickness of the metal and can provide protection for between 10-20 years if the cathodic protection is not interrupted.
A general discussion of inhibiting corrosion in reinforced concrete is found in U.S. Pat. No. 5,183,694 (Webb) from corrosion caused by strong Lewis bases, such as chloride ions and/or a loss of pH to below 10 and from corrosion caused by carbonation of the concrete by penetration of carbon dioxide from the atmosphere.
A second discussion of the effects of cathodic protection is found in U.S. Pat. No. 5,225,058 (Bazzoni et al.), where concern about hydrogen embrittlement is addressed when high tension steel in prestressed concrete structure is protected by a powered system.